1. Field of the Invention
One aspect of the present invention relates to a wavelength selective switch.
2. Related Background Art
A device which controls an optical path by independently performing modulation based on a diffraction-grating-shaped phase modulation pattern on each wavelength component using an optical phase matrix device having a grating structure is disclosed in US Patent Application Publication No. 2006/0067611.
A wavelength selective switch includes a wavelength selective switch using a phase modulation element. The phase modulation element is an element including a plurality of pixels arranged in a two-dimensional shape and capable of performing phase modulation in each pixel. In such a wavelength selective switch, a light input/output port which is a coupling destination of each wavelength component is selected by presenting a diffraction-grating-shaped phase pattern to the phase modulation element and controlling a reflection direction of each wavelength component incident on the phase modulation element.
Usually, when light is incident on the diffraction grating, a plurality of light components, such as a zero order light, ±1st order light, ±2nd order light . . . , are generated. Among them, since a light intensity of the 1st order light is highest, the 1st order light is coupled to an output port. However, light intensities of other diffracted lights such as the zero order light or the −1st order light may increase depending on the precision of a phase modulation pattern such that the light intensities cannot be neglected. Particularly, the −1st order light is generated at an output angle symmetrical to that of the 1st order light. Therefore, the −1st order light is incident on other light input/output ports and causes noise light depending on an arrangement of the light input/output ports.